DESCRIPTION (based on the Abstract): The intracellular phase of the life- cycle of the human immunodeficiency virus type 1 (HIV-1) and other retroviruses begins with synthesis of viral DNA and its integration into the host cell chromosome. Recent data indicate that reverse transcription of HIV- 1 DNA is not completed after infection of quiescent lymphocytes.Instead, a unique, latent, labile replication intermediate is established in which the HIV-1 genome is present in a partially reverse transcribed form consisting of both RNA and DNA. If the infected quiescent lymphocytes are activated by exposure to mitogens, reverse transcription is resumed and the cells produce progeny virus. Since most (more than 99 precent) circulating CD4+ lymphocytes are quiescent, they may act as an inducible reservoir of virus. The functional lability of this HIV-1 intermediate in quiescent lymphocyates may in part explain the long period of clinical latency that precedes development of the acquired immunodeficiency syndrome (AIDS). The experiments proposed should elucidate the structure and fate of this novel viral replication intermediate. Using a variety of preparative techniques, intracellular particles will be recovered from quiescent lymphocytes for molecular analysis. Their structures and protein composition will be examined using ultracentrifugation, immunoprecipitation and nuclease probes. The functional stability of these complexes will also be assessed in a cell-free reverse transcription system, and by reintroducing these particles into permissive cells. Examination of the functional and structural properties of the HIV-1 intermediate in quiescent lymphocytes will provide new insight into viral persistence and virus-host cell interactions. In addition, understanding the processes responsible for the structural and functional lability of these particles in quiescent cells may suggest new therapeutic strategies for HIV infection, based on preventing establishment of the provirus in newly infected cells.